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A371935
Decimal expansion of Sum_{k>=0} (-1)^k / ((k+1)*(2*k+1)!).
1
9, 1, 9, 3, 9, 5, 3, 8, 8, 2, 6, 3, 7, 2, 0, 5, 6, 5, 1, 9, 8, 1, 2, 6, 7, 8, 5, 1, 1, 4, 0, 4, 6, 7, 9, 2, 5, 3, 5, 3, 7, 9, 1, 5, 8, 7, 6, 4, 1, 5, 5, 5, 4, 4, 6, 5, 9, 8, 0, 5, 4, 8, 9, 2, 3, 7, 7, 9, 9, 2, 1, 0, 4, 5, 1, 0, 5, 6, 4, 7, 0, 9, 6, 4, 0, 9
OFFSET
0,1
FORMULA
Equals 2*(1 - cos(1)) = 2 * A371936.
From Hugo Pfoertner, Apr 26 2024: (Start)
Equals A243596/Pi.
Equals A272795^2. (End)
EXAMPLE
0.91939538826372056519812678511404679253...
MATHEMATICA
s = N[Sum[(-1)^k/((k + 1) (2 k + 1)!), {k, 0, Infinity}], 120]
First[RealDigits[s]]
CROSSREFS
KEYWORD
nonn,cons
AUTHOR
Clark Kimberling, Apr 24 2024
STATUS
approved